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 Post subject: Frequency Counters
PostPosted: May Wed 22, 2013 3:22 am 
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Location: Fulton missouri
I would like to buy a counter to check the frequency of an Eico 315 signal generator. I am looking for something simple and as inexpensive as possible. I may put a want ad in the classified section, but for now am looking for suggestions on what makes and models I should look for. I saw on here before where a digital a.m. radio could be used to check calibration? Could someone elaborate on using a digital radio or would a frequency counter be the better option. Thanks


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 Post subject: Re: Frequency Counters
PostPosted: May Wed 22, 2013 4:23 am 
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This is what I have:
http://www.ebay.com/itm/Heathkit-IM-410 ... 4172a45491
this model is quite plentiful on E-Bay---average price is probably a bit higher than the one in the link.

using a digital radio:
Put the radio close enough to the signal generator output cable so that you hear the signal on the radio. Set the radio the desired frequency, then tune the generoator for maximum signal.

If you don't already have a digital radio, I'd just get a counter.

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 Post subject: Re: Frequency Counters
PostPosted: May Thu 23, 2013 12:07 am 
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There are a few minor "gotchas" that pop up when you try to connect a frequency counter to a signal generator such as this:

1. You normally use very low output levels for aligning radios, on the order of a few millivolts or microvolts. Many counters require tens or hundreds of microvolts of signal before they lock up. This means that you either have to add a high level output jack to the signal generator, or adjust the output level up and down every time you want to take a frequency reading.

2. Many signal generators of this type do not produce sufficient RF output, or waveforms that are too distorted, to reliably operate some kinds of frequency counters. The problems are usually worse on the highest frequency band.

3. The frequency counter probably won't work if the modulation in the signal generator is turned on, but you need modulation for most AM alignments.

None of these problems occur if you tune the generator against a good quality digital radio.

But the digital radio method has a few limitations too:

1. It is hard to do if the frequency you want happens to be near stations that are on the air. You'll get lots of birdies and heterodynes unless you disconnect or defeat the antenna in the radio so it doesn't pick up outside stations, but it still has to have enough sensitivity to pick up the signal generator. Not all digital radios are designed so you can remove or disable their antennas easily.

2. Most digital radios do not cover all the frequencies of interest. For example, 450 kHz to 500 kHz (IF frequency range) is not often available. What you have to do is set the radio to the second harmonic of the frequency you want (eg. set the generator to 455 kHz and tune it in on the radio at 910 kHz). Problem with this approach is the second harmonics are usually much weaker than the fundamental frequencies, and therefore harder to tune.

3. Unless you are talking about a very high end (and expensive) digital communications receiver, digital radios are not as precise as most frequency counters are. And it's hard to get closer than a couple hundred Hz by ear in any case. Now this is still perfectly acceptable for aligning antique household radios, but probably not so good if you do higher precision work.

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 Post subject: Re: Frequency Counters
PostPosted: May Thu 23, 2013 4:16 pm 
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Chris108 wrote:
unless you disconnect or defeat the antenna in the radio so it doesn't pick up outside stations, but it still has to have enough sensitivity to pick up the signal generator. Not all digital radios are designed so you can remove or disable their antennas easily.


Use a car radio and don't plug the antenna in, this way your reception will be much reduced and be much more local.

I have one mounted on my work bench as a source of entertainment, signal source through the amp outputs for modulation and testing amps I'm working on. I have a tone generator CD, that has discrete frequencies as well as sweeps.

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 Post subject: Re: Frequency Counters
PostPosted: May Fri 24, 2013 1:59 am 
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I would like to ask a related question. What is the best way to confirm the frequency of a sweep generator? I put my Precision E-410C on my Fluke 7220A frequency counter and it jumps around too much for me to conclude anything definitive (even with the sweep width turned all the way down). For example, if I put the sweep generator on 40 Mhz, the Fluke will jump between 19.877 Mhz and 21.653 Mhz. I can explain away the halving of the frequency due to blanking pulses, but the variation is too flukey (no pun intended).


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 Post subject: Re: Frequency Counters
PostPosted: May Sat 25, 2013 11:34 pm 
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A decent digital radio which can be bought reasonably would be the Radio Shack/Realistic DX-390.

It covers 150 KHz to 30 MHz plus FM Broadcast band 88-108. Plus, while it may not be the best receiver, its good enough for portable SW listening and DXing. Or just a casual radio while you work. :D

-Steve


Attachments:
dx-390.jpg
dx-390.jpg [ 169.89 KiB | Viewed 891 times ]

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 Post subject: Re: Frequency Counters
PostPosted: May Sat 25, 2013 11:49 pm 
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Chris108 wrote:
There are a few minor "gotchas" that pop up when you try to connect a frequency counter to a signal generator such as this:

1. You normally use very low output levels for aligning radios, on the order of a few millivolts or microvolts. Many counters require tens or hundreds of microvolts of signal before they lock up. This means that you either have to add a high level output jack to the signal generator, or adjust the output level up and down every time you want to take a frequency reading.

2. Many signal generators of this type do not produce sufficient RF output, or waveforms that are too distorted, to reliably operate some kinds of frequency counters. The problems are usually worse on the highest frequency band.

3. The frequency counter probably won't work if the modulation in the signal generator is turned on, but you need modulation for most AM alignments.


Chris makes some valid points here.

As long as one is cognizant of these elements they don't really present a problem, as such, at all.

I bought a GWbrand (Model GFC-8010-G) 100Mhz Freq Counter on Ebay for about $40 some years ago. Works perfectly.
I keep my digital freq counter connected to the Sig Gen's RF output connector with a BNC tee connector.

1.) I turn up the output level to a higher setting when selecting the freq so the counter can sense it. After the proper freq is selected the gain is turned down.

2.) This hasn't been a problem yet that I've encountered with my sig gen and freq counter combination.

3.) The modulation must be turned off while reading the freq. I only turn modulation on after selecting the freq.
You do not need modulation for most IF alignments if you monitor the AVC line while aligning.
But it doesn't present a problem anyway because the modulation is only turned on after the freq has been selected.

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Last edited by Pbpix on May Sun 26, 2013 8:35 am, edited 2 times in total.

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 Post subject: Re: Frequency Counters
PostPosted: May Sat 25, 2013 11:54 pm 
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Once you "loosen up" an oscillator so it sweeps well, it is awfully hard to get it to sit still long enough to measure it with a frequency counter. High end lab sweep generators can do it, but it's a lot to ask from a service grade unit. After all, in use, they are expected to provide a range of frequencies wider than what you are trying to align, not a single precise frequency.

Sweep generators fall into two classes, those where you set a center frequency, and the generator sweeps above and below that by a certain amount, and ones where you set start and stop frequencies. You can verify that they are working correctly by tuning the expected sweep range on a digital radio. Doing it with an oscilloscope, marker generator (with crystals if possible) and detector--just as it would be in an actual sweep alignment--is probably the best verification.

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 Post subject: Re: Frequency Counters
PostPosted: May Sun 26, 2013 12:13 am 
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Clint wrote:
I saw on here before where a digital a.m. radio could be used to check calibration? Could someone elaborate on using a digital radio or would a frequency counter be the better option. Thanks

I guess it would depend on what you were primarily wanting to calibrate. If lab or communications type equipment, perhaps the counter might be the best option.

OTOH, for AM/FM radios, a digital readout radio I have found to work perfectly well.

I have a Rat Shack "DX-395" that I picked up on eBay some years back for small change (less than 10 bucks) which works perfectly well for the AM and FM broadcast band frequencies. It's SW band will even cover the FM IF freq of 10.7 Mhz, although I've never tried it. Simply laying the probe from the generator next to it will produce the tone.

Another use for it is to verify accuracy in tracking on the radio under test from broadcast stations, without using a generator. I just find this a more enjoyable way of testing.

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 Post subject: Re: Frequency Counters
PostPosted: May Sun 26, 2013 12:17 am 
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Chris108 wrote:
Once you "loosen up" an oscillator so it sweeps well, it is awfully hard to get it to sit still long enough to measure it with a frequency counter. High end lab sweep generators can do it, but it's a lot to ask from a service grade unit. After all, in use, they are expected to provide a range of frequencies wider than what you are trying to align, not a single precise frequency.

Sweep generators fall into two classes, those where you set a center frequency, and the generator sweeps above and below that by a certain amount, and ones where you set start and stop frequencies. You can verify that they are working correctly by tuning the expected sweep range on a digital radio. Doing it with an oscilloscope, marker generator (with crystals if possible) and detector--just as it would be in an actual sweep alignment--is probably the best verification.


Sweep generator?
I didn't think a freq counter could be used to read a sweeping signal anyway.
The op is looking for a freq counter to read the Eico 315
Is the 315 a sweep generator too? I'm not familiar with that model.

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 Post subject: Re: Frequency Counters
PostPosted: May Sun 26, 2013 1:01 am 
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The EICO 315 is just a standard AM generator.

Not many sweep generators are made for AM broadcast radio IF alignments. It would be best to use a more modern digitally controlled generator for that purpose.

Oh, btw, I could also mention the Radio Shack DX-392 which is the same as the DX-390 except it has a built-in cassette recorder. Kinda handy in that respect! :)

-Steve

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 Post subject: Re: Frequency Counters
PostPosted: May Sun 26, 2013 1:57 am 
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Location: Long Island
Quote:
Sweep generator?
I didn't think a freq counter could be used to read a sweeping signal anyway.
The op is looking for a freq counter to read the Eico 315
Is the 315 a sweep generator too? I'm not familiar with that model.


I was replying to Stephen, who asked about verifying the frequency of a Precision E-410C sweep generator as a related question. He's not having much luck using a frequency counter on it, and I was attempting to explain that's par for the course.

The Eico 315 at the top of the thread is an AM/CW RF alignment generator, non-swept, with a very big and elaborate dial.

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 Post subject: Re: Frequency Counters
PostPosted: May Mon 27, 2013 2:58 am 
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Joined: Jan Thu 01, 1970 1:00 am
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Location: Haledon NJ USA
We have a local station here at 910 AM. If I tune any old radio to 910, and I get my old signal generator tuned for exactly 455 KHZ, it is at zero beat with the radio (455 + 455 = 910). I believe I learned that reading Elements Of Radio Servicing.

Ken D.


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 Post subject: Re: Frequency Counters
PostPosted: May Tue 28, 2013 1:35 am 
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The Rat Shack radio was a great idea - especially since I have one in the closet! It is a new Grundig with a digital readout. I now have it on my equipment shelf. Thanks!


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 Post subject: Re: Frequency Counters
PostPosted: May Tue 28, 2013 9:31 pm 
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...and a radio with SSB (Degen/Kaito 1103 for example) makes it easier to hear the carrier whistle rather than the modulation.

I use a Kenwood R2000 comms receiver with the antenna lead near the sig gen - no local signals to confuse the issue!

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